Structure for use in an electrodynamic transducer



March 27, 1962 w. T. HARRIS 3, 7,

STRUCTURE FOR USE IN AN ELECTRODYNAMIC TRANSDUCER Filed Feb. 24, 1960//3 w //z Z IN VEN TOR. W/ 8M? 77 697 6 45 ayg/umkM/m 3,027,541 PatentedMar. 27, 1962 3,027,541 STRUCTURE FOR USE IN AN ELECTRO- DYNAMICTRANSDUCER Wiibur T. Harris, Woodbury, Conn., assignor to The HarrisTransducer Corporation, Woodbury, Cornn, a

corporation of Connecticut Filed Feb. 24, 1960, Ser. No. 10,587 4Claims. (Cl. 340-42) My invention relates to structures for use inelectroacoustic transducers suited to underwater operation.

This application is a continuation in part of my prior applicationSerial No. 241,470 of August 11, 1951, en-

titled, Electrodynamic Transducer, now Patent No. 2,978,671 of April 4,1961.

In the said prior application Serial No. 241,470 (now Patent No.2,978,671) a number of transducer constructions are disclosed in whichthe vibration-producing elements are supported on bodies ofsound-attenuating material or the like, and in which certain improvedstructures are disclosed for providing a magnetic circuit within whichthose vibration-producing elements are supported. The present inventionrelates to a magnetic stmcture per se, suitable for use in anelectroacoustic transducer of the type under discussion, and isspecifically disclosed in an embodiment in which the vibration-producingelements are not mounted on sound-attenuating bodies. The arrangement ofthe parts of the structure of the present in vention produces astructure which is electromagnetically Effective, reliable, and readilymanufactured and assem- 1 ed.

It is, accordingly, an object of the invention to provide an improvedstructure for use in a transducer of the character indicated.

It is another object to provide a transducer having high efficiency overan extended frequency range.

It is a further object to provide an improved non-resonant transducer.

Another object is to provide an improved, relatively highly efiicienttransducer for electroacoustic or acoustoelectric conversion in waterand having further useful application in air.

Other objects and various further features of novelty and invention willbe pointed out or will occur to those skilled in the art from a readingof the following specification in conjunction with the accompanyingdrawings, in which the figure is a fragmentary cross-sectional view of apreferred embodiment of the present invention.

As has been stated above, the embodiment in the figure discloses atransducer in which the active vibration-producing strips 1% are notsupported on bodies of sound attenuating material or the like, but whichembodies an effective and efficient and magnetic circuit arrangement.The active strips 100, laminated to reduce eddy current losses, areinterposed between the bar magnets 192 which are polarized and arrangedas shown. The magnets 102 are secured in any appropriate manner tosupporting struts 1% of non-magnetic material which extend between themagnets 102 and a bottom plate 106 of magnetic material. The struts 104are provided with central openings 198 in order that the spaces betweenthe struts 104 may communicate with one another. The magnetic bottomplate 186 is provided with an upstanding end wall 110, preferablyintegral therewith, which is also formed of magnetic material and withwhich the end magnet 102 is in operative magnetic connection, as byabutting directly thereagainst. The bottom wall 106 may be provided witha plurality of openings 112 therethrough communicating between the loweredge of the bottom plate 106 and the spaces between the struts 104. Theentire assembly is surrounded by an acoustically transparent rubbersheath 114, the conductive strips being mounted directly on theunderside of the upper portion of that rubber sheath 114 in anyappropriate manner so as to be operatively interposed between theopposite magnetic poles of a pair of magnets 102. The interior space ofthe transducer of the figure is adapted to be filled with a liquid,which may have an acoustic impedance equal or close to that of water,although water itself is not preferred for reasons which are notacoustic in nature, such as lack of insulative properties and tendencytoward corrosion. Accordingly the filling liquid is preferably a lowviscosity liquid having good electrical insulating properties, such as alow molecular weight" silicone fiuid. The active strips 1% are, ofcourse, formed of electrically conductive material, such as copper. Theymay be electrically connected in parallel to a suitable source ofelectrically, but since this would make for unduly low electricalimpedance, I prefer that they be series connected. The openings 112 inthe bottom wall 106 permit acoustic radiation through that bottom wall,and also provide for pressure compensation, so that the active strips100 will remain properly positioned within the air gaps between themagnets 102 substantially independent of the depth beneath the surfaceof the sea at which the transducer is operating. The magnetic circuitextends straight across the top of the device from one magnet 102 to theother, and therefore directly across the gaps in which the active strips11%) are located, the return magnetic path being defined by thesubstantially continuous end wall 110 and bottom wall 1&6, which areformed of magnetic material as aforesaid.

It will be seen that I have described novel acoustoelectric andelectro-acoustic transducer means applicable to air and water use. Theconstruction provides especially advantageous underwater features,including great power-handling capacity over a relatively broadfrequency band. The basic construction is relatively simple and lendsitself to arrays of almost any desired configuration.

While I have described my invention in detail for the preferred formsshown, it will be understood that modifications may be made within thescope of the invention, as defined in the following claims.

I claim:

1. In a transducer of the character indicated, a series magnetic circuitcomprising a series of spaced bipolar permanently magnetized elementsdefining a series of polarized gaps, ferromagnetic means independent ofsaid permanently magnetized elements interconnecting the outer ends ofthe outer of said elements, whereby the series magnetic circuit may beclosed, and electrically conducting means movably supported in the gapsbe tween said elements, in which said ferromagnetic means comprises apart extending beneath and spaced from said magnetized elements, andnon-magnetic means interposed between and engaging said part of saidferromagnetic means and said magnetized elements and constitutingsupports for the latter on the former.

2. The transducer of claim 1, in which said non-magnetic means onlypartially fills the space between said magnetized elements and saidferromagnetic means, and a liquid filling the remainder of said space.

3. In a transducer of the character indicated, a housing comprising sideand bottom walls of ferromagnetic material, a series magnetic circuitcomprising a series of spaced bipolar permanently magnetized elementsacross the top of said housing defining a series of polarized gaps, theoutermost of said permanently magnetized elements being magneticallyoperatively connected to the side walls of said housing, said side andbottom walls of said housing defining a ferromagnetic means independentof said per- References (Zited in the file of this patent UNITED STATESPATENTS Evershed et :11. Mar. 9, 1920 Riegger Oct. 26, 1926 VasilachAug. 18, 1942 Olson Oct. 14, 1947 Merten Dec. 6, 1949 Bardeen et a1Sept. 6, 1955

